In semiconductor process technology, planar substrate surfaces which are horizontal with respect to a wafer surface are patterned by photolithographic methods in combination with selective etching processes. During the processing of integrated circuits, reliefs with a pronounced topography are formed on the wafer or substrate surface. A relief of this type also has surfaces which are inclined or vertical with respect to the substrate surface. As part of the ongoing shrinking of the integrated circuits, it is necessary for vertical or inclined process surfaces to be patterned as well, in order for it to be possible to functionally differentiate the structures over their vertical extent. Examples of such structures include deep trench capacitors, stacked capacitors and vertical transistor designs.
It is not directly possible to pattern reliefs in a direction which is vertical with respect to the substrate surface by means of photolithographic methods. Vertical patterning of this nature is usually carried out with the aid of a suitable filler material which, as a mask, covers regions of the relief located beneath a coverage depth during processing of unmasked regions. In this case, patterning of a relief in a direction which is vertical with respect to the substrate surface, with regard to a coverage depth which is selected as desired between a substrate surface and a relief depth, then usually takes place using one of the following methods.
In a first method, where an oxide is to be deposited exclusively in a lower region, arranged between the coverage depth and the relief depth of a relief, in a first step an oxide is deposited or produced over the entire surface of the relief. Then, the relief is initially completely filled with a suitable filling material, and then the filling material is recessed back to the coverage depth. Then, uncovered sections of the oxide are removed, and as the final step residual sections of the filling material are removed altogether.
In a second method where an oxide is to be deposited or produced only in upper regions, arranged between the substrate surface and the coverage depth of a relief, an etching stop layer (e.g., a nitride layer) is first provided over the entire surface of the entire relief. This is then followed by filling of the structure with a suitable filling material (e.g., polycrystalline silicon) and etching back of the filling material as far as the coverage depth. Then, the etching stop layer is removed in the unmasked sections and an oxide is deposited or generated by thermal means in the uncovered regions. Next, the oxide is anisotropically etched. This is followed by removal of the filling material and, as a final step, the complete removal of the etching stop layer.
In addition, plasma-enhanced chemical vapor deposition (PECVD) processes are known. In these processes, thin films, the thickness of which on surfaces which are vertical or inclined with respect to the substrate surface decreases as the depth increases, are produced on surfaces of a relief. However, in this process it is difficult to control the way in which the layers produced end in the depth direction. Furthermore, layers of this type have very considerable differences in thickness between an end point in the depth and a region close to the substrate surface.
Likewise, in the case of diffusion-limited deposition of silicon oxide by means of tetraethyl orthosilicate (TEOS), the silicon oxide grows on surfaces which are inclined or vertical with respect to the substrate surface at a rate which decreases as the relief depth increases, and consequently the layer thickness of the silicon oxide produced in this way decreases in the direction of the relief depth.
Therefore, there have hitherto only been complex processes which allow a covering layer of uniform layer thickness to be arranged or produced exclusively above or below a coverage depth on surfaces of a substrate which are vertical or inclined with respect to the substrate surface.